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Hugh Pickens writes "Charles Q. Choi reports that hairspray could one day serve as the sign that aliens have reshaped distant worlds because one group of gases that might be key to terraforming planets are CFCs. 'Our hypothesis is that evidence of intelligent life might be evident in a planetary atmosphere,' says astrobiologist Mark Claire at the Blue Marble Space Institute of Science. CFCs are entirely artificial, with no known natural process capable of creating them in atmospheres. Detecting signs of these gases on far-off worlds with telescopes might serve as potent evidence that intelligent alien civilizations were the cause, either intentionally as part of terraforming or accidentally via industrial pollution. 'An industrialized civilization will be one that will use its planetary resources for fabrication, the soon-to-be-detectable-from-Earth atmospheric byproducts of which could be a tell-tale sign of their activity,' says astrobiologist Sanjoy Som. CFCs can be easily recognized in planetary atmospheres because their atmospheric 'fingerprint' (i.e. chemical spectra) is very different from natural elements, and are a tell-tale sign that life on the surface has advanced industrial capabilities. Using state-of-the-art computer models of atmospheric chemistry and climate, researchers plan to discover what visible signs CFCs and other artificial byproducts of alien terraforming or industry might have on exoplanet atmospheres. 'We are about a decade away of being able to measure detailed compositions of the atmospheres of extrasolar planets,' says Som."

Detecting CFCs applies well if you imagine that aliens are human-like. But real aliens can in reality substantially different than humans. The Universe is weird enough to allow some surprises.

I've read some news about some odd planets floating somewhere. One planet is almost entirely sugar, and there's some sort of nebula that is basically alcohol. Life could be present in these odd places, and the way life manifests itself might be totally different from what we see here on Earth.

So yes, CFC is a good sign, but aliens might be much weirder and let's not expect that they follow the same patterns as we do. I mean, aliens don't need hairspray.

What makes you think that life on another planet won't have found some biological use for CFCs?

Oh man, talk to a chemist, they are inert, which makes things biologically complicated and the precursors are beyond nasty. For a good time google for Bromotrifluoromethane Synthesis (aka what you non-chemists would call "Halon") and imagine what it takes to make it both industrially and almost unimaginably via biosynthesis. Its not so much the final step that's the problem, but the precursors, processing the raw materials, etc.

Its not for lack of evolutionary pressure. Plenty of vessels and orifices would benefit by a native layer of teflon. Imagine the predator prey relations in a world of teflon skin. Some of the room temp liquid CFCs would superficially make a good replacement for that fluid in the bone joints (sorry not doc don't know its technical name).

Theres also some evolutionary pressure in that you'd need a species that eats flourite ore rocks (or at least stuff grown in its soil, or naturally heavily floridated water) AND in the halon example a biological bromine source... One or the other, OK, but at this time of day I can't think of a way to pull off both. Some kind of migratory coastal ruminant mammal? Um...

Also there's some thermodynamics issues, if you could pull off the synthesis in a cell, it would need to be a better idea than simply synth more ATP or hemoglobin or whatever else... Need to find a bio app where CFCs are more beneficial than anything else a cell can synth. CFCs are expensive to make so you need a good reason. Much as superficially silicon based brains "seem" more sensible than neuron based brains but its so hard to make a self reproducing factory the size of a typical mammal womb that its not happening any time soon.

To some extent thats why halon is such a good fire extinguisher around humans. Terrestrial biochemistry has almost no idea how to interact with it, so it pretty much doesn't. CFC suffocation is a zillion times more likely than CFC poisoning. I was told but am too lazy to verify that if you get CFCs into your blood your kidneys get somewhat confused.

Oh man, talk to a chemist, they are inert, which makes things biologically complicated and the precursors are beyond nasty.

Perhaps I'm not up to speed on chemistry, but that's only true for the industrial processes that we use. The only ways we can fix nitrogen are currently pretty biologially unfriendly at the moment.

Biological tissue has severe issues dealing with fluorine ions, which is too bad.

True, but some organisms have evolved to deal with it. For instance monofluoroacetate can be produced biologically.

The point is that life on other planets may be quite different from our own. It will probably be based on carbon, since nothing else is nearly so flexible, but I don't see any reason why the chemistry should be anything close.

Plenty of vessels and orifices would benefit by a native layer of teflon.

Quite possibly, though the ability to synthesize some fluorine containing chemicals doesn't indicate the ability to synthesize them all. Also, don't forget that the parts have to be repairable and also have to have wound up there by evoloutionary chance as well.

Very many things end up down a sub-optimal branch from which they cannot escape.

Evolution would suggest that its biochemistry would probably be very much like that of earth life, since evolution favors the "path of least resistance" - biochemistries unsuited for survival will tend to die off, biochemistries efficient at survival will tend to flourish.

Consider the wavelengths of light absorbed by Earth's photosynthesizing plants. Now consider the wavelengths NOT absorbed by plants. These rejected wavelengths (green, mostly) are actually the most abundant, so it is counterintuitive that plants would evolve to effectively discard a useful energy source. It is very odd when you consider that pretty much every bit of free energy is capitalized by some form of life, yet the most abundant wavelengths are rejected.

The going theory is that originally archaea DID make use of the green wavelength and didn't waste energy trying to capture the less valuable reds and blues. Cyanobacteria's ancestors (and the predecessor to our modern green plants) is theorized to have taken advantage of this 'discarded' spectrum where competition was lessened.

Big deal, you may think. However, when you realize that our planet is pretty 'green' rather 'purple' you have to come to terms with the fact that the dominant plant life on Earth actually evolved along the more difficult path, scrounging 'scrap' energy. We aren't completely sure WHY cyanobacteria beat out archaea, because if you were to look at it from an unbiased perspective when life first emerged on the Earth, a betting man would have bet on archaea. It had monopolized the most valuable wavelengths in terms of available energy, was fairly dominant, and by all typical measures, was more 'fit' to its environment. Theories abound that perhaps being forced to use the 'dregs' of light forced early cyanobacteria to be more efficient in its energy usage, evolving processes which wasted less, allowed simpler reproduction, etc, and then a global stressor caused the purple life to falter, the green life took up the slack and never gave back its dominant position.

There are lots of theories to why, but the important fact here is that for some reason, the less likely lifeform became dominant.

Evolution would suggest that its biochemistry would probably be very much like that of earth life,...

only because the terrestrial evoltionary process is biased by being immersed in a watery environment. I fail to see that a water-chemistry evolution would be optimal on a planet brimming with liquid ammonia or liquid hydrocarbons.

For life to even stand a chance, you're going to need readily available raw materials, a "solvent" that's compatible (chemcally) with the raw materials, and an energy transf

It's not for lack of evolutionary pressure. Plenty of vessels and orifices would benefit by a native layer of teflon. Imagine the predator prey relations in a world of teflon skin. Some of the room temp liquid CFCs would superficially make a good replacement for that fluid in the bone joints (sorry not doc don't know its technical name).

Synovial fluid. [wikipedia.org] Sidenote, evolution tends to not reinvent the wheel, even if reinventing the wheel is entirely possible. Even if CFCs were possible to chemically make inside the body, I think evolution would tend to tweak it's fluid, protein, and connective tissue to make synovial fluid rather than make a new pathway for making CFCs.

The human brain for example is in many ways just a reptilian brain with some add-ons. Important ones, but the brain was not totally overhauled.

No, but I'd wager most of them revolve around using bone and muscle to move the predator to the impala and then using some sharp bit of bone or keratin to shred and kill it. There are many diverse ways within that, but nature generally doesn't totally reinvent the basics. I haven't heard of any natural predators that use projectiles shot from their bodies, or clouds of knockout gas, for instance. It would require quite a bit of evolutionary innovation and then refinement for any of those to become useful

No, in other words diversity doesn't happen equally fast at all possible levels. Perhaps a better example would be DNA coding. How the DNA is read stays very consistent [biomedcentral.com]. I don't believe there's any chemical reason why AUG MUST be translated as methionine. You could have AUG read as any other amino acid. But if you made that change suddenly, none of your existing protein sequences would work, and you would go extinct immediately.

Gould calls these things constraints on evolution. There are a number o

If a planet had a significantly different ratio of base elements, such as a lot of fluoride and bromide on its surface, I assume life would make use of it and arrive at what you describe as 'teflon shells'. After all life here makes lots of things which are a LOT more complicated.

So the real question is: can a planet form with widely different ratios of elements on its surface (who cares what's at the core) ? Or do planet formation models lead to gaseous / rocky worlds which have basically always

I'm not sure what you're getting at. For the chemistry at the surface of a planet, then yes, you couldn't care less what's in the core ; but if you care about little things like having an atmosphere, then the core matters, because you need the mass to provide the gravity.

The composition of the Earth (and of all planets studied in any great detail) can be described to a reasonably good approximation by taking a nucleosynthesis distribution (i.e., what is produced when a supernova goes "bang" with around 10^

What makes you think that they will discover something significantly different from CFCs as an inert propellant?

The simplest reason: They have significantly different materials to work with, affected by a different degree of planetary gravity (if that's relevant to what they're building), because they're on a different planet.

There are a limited number of ways to solve a problem given these constraints. Regarding the GP - this can be used for a lot more than hairspray.

Generally, if we look at enough of our industrial output, there should be some overlap with any arbitrary sentient species.

What is more of a concern... 500+ light years away, another alien civilization is looking at Earth, and not detecting squat, as we look at them, and don't detect squat. By the time evidence of civilization from either pl

I believe that certain extreme environments *could* change the kinematics of chemical reactions. Take very strong magnetic fields, for example. These tend to deform the electron shells, and since these dictate chemical reactions, I'd be surprised if these were unaffected.

But, granted, extreme environments are probably not conducive to the emergence of life in the first place.

Well, the question you gotta ask is the opposite. What if the physics of a distant galaxy is different from the one around here?

Well then I guess that its spectral lines might be different. And its movement in space might be different.

We can now see more or less to the edge of the observable Universe which happens to be also a picture form the very distant past. Yes, the Universe looked different back then, of course it does, but the light we see is still the same. The nature of light includes in itself qui

Exactly! All this science stuff is just humbug malarkey spread by all e college people who like to flaunt their learning as they drive past in their Suburus. And the only thing worse than an college person are those dirty worker types, all ignorant and stupid and stuff. Nope, the only people you can trust are those that wear nice suits, drive nice shoes, and wear nice cars. the sorta people you find running Wall Street. Their the last, best hope for hoomanity!

Physics does not say WASP-1b cannot exist, just that it's not going to stay where it exists for very long.

Physics does not say the moon is "too big", it says that the moon is of a size that makes it unlikely to have been a passing object "captured" by the Earth's gravity.

The age of the dust on the moon is accountable by the simple and obvious fact that much of it did not originate from the moon's rocks, which are younger. This fits in nicely with the moon not being a captured satellite.

true, but for intelligent life you need a body and appendages. you need hands and fingers to manipulate your environment like humans use hands to make tools. other animals use flora to make nests and dams but the fact that they can't use their hands and fingers like us limits them.

in order to get to the high tech part of life you need body parts to manipulate your environment in low tech ways to make the tools and machines to allow you to progress in technology

An alien civilization might use them for terraforming (or Xanthaforming) new homes.

My question is: Why would they terraform at all?Any civilization capable of meaningfully terraforming a planet is bound to be capable of not having to live on a planet or not having to care whether there is oxygen and atmospheric pressure on it.

Variety. Think, if human kind got the capability for cheap inter-planetary travel there'd be colonies in all kinds of environments, asteroids, comets, various gas giant satellites and any easy to terraform planets. Different people like different things.

I know the whole space-station/asteroid colony thing is cool, but planets have several advantages

1) Your survival is not dependent on the continuous operation of high technology devices - especially important if you're thinking in terms of millenia and insuring your descendants survive even if they pass through some form of knowledge-sapping Dark Ages.2) They're big, and virtually indestructible.3) Any ecological catastrophe is likely to proceed slowly (see 2), likely giving you decades or centuries of to develop a fix rather than the hours or months likely in an artificially constrained ecosystem.4) They're far more suitable as a "genetic heritage" site if you want a large, chaotic system of thriving genetic diversity5) Lots of people might well prefer to live within a thriving ecological web than in a rigorously controlled environment. I know I would.6) And possibly most importantly, if you have suitable candidates terraforming a planet is probably one of the most cost-effective ways to support billions of individuals. In fact the up-front costs of converting Venus (Mars is a much tougher nut to crack) into something way more hospitable than an asteroid are probably negligible - design a bacterium that will thrive in the current environment and bind atmospheric carbon dioxide into some stable solid, then seed the planet with them and wait a few centuries. Sure it takes a while, but it's a grad-student synthetic biology project with extra credit for having your bacteria designed to die off as conditions approach Earth-norm. Heck, we're almost to the point of being able to do such things ourselves. And once you've got a planet in the proper temperature range with a "non-hostile" atmosphere seeding it with "normal" bacteria to add proper amounts of oxygen and establish a thriving microbial biome in which multicellular life can thrive, while perhaps more challenging, is still potentially a research-project level endeavor whose expense will trivial compared to say, building an interstate highway. So basically, given cheap interplanetary travel all you need is a few individuals with vision to work on a centuries-long project and you can quite possibly terraform an "easy" planet to the point that people could walk unprotected outdoors and establish homesteads, even if they have to import their own multicellular life.

Meanwhile building a viable enclosed ecosystem even the size of a small city is likely to be an extremely expensive undertaking, especially when you factor in radiation shielding, meteor defense systems, etc. Not to mention gravity - tethering is relatively cheap, but enough cable to support a city (plus shielding) under anything approaching Earth-norm accelerations is still going to be impressive, not to mention you have to perform ongoing maintenance continuously. Perhaps the whole thing could be done organically as some sort of city-sized organism/symbiosis, but that's supposing a much more advanced level of biotechnology, and you'd still have to feed the thing as it grows, though ideally it could absorb sunlight and some convenient carbonaceous asteroids for most of it's needs.

CO2 isn't the biggest problem terraforming Venus, but even the CO2 problem probably can't be solved with just bacteria. Carl Sagan was one of the original proponants of that idea, but after further study, he conceded that it wouldn't work because of thermodynamics (it's currently just too hot, you must first cool it down to make those reactions stable).

Changing the day/night ratio to something reasonable and establishing some sort of magnetic field to block out solar radiation would probably also be requir

But CFCs are not something that occur in nature by any process we know, and thus if we see them in abundance where they should not be, that's a sign something very interesting is happening there, caused by something that is worth investigating. Maybe it's aliens, maybe it's a new natural phenomenon.

Wait, they could be "a sign" but not a "conclusive sign" of technological processes? Since when does science give us maybes and variables? Science is supposed to be like the bible: clean, concise, and unambiguous!

CFCs can be easily recognized in planetary atmospheres because their atmospheric 'fingerprint' (i.e. chemical spectra) is very different from natural elements, and are a tell-tale sign that life on the surface has advanced industrial capabilities.

Are these CFCs made from exotic kinds of matter? Are we looking for advanced civilizations that have been able to synthesize new forms of chlorine, fluorine, carbon, etc., that are different than those that arise from stellar nucleosynthesis? No? In that case,

.... atmospheric 'fingerprint' (i.e. chemical spectra) is very different from natural elements

Are these CFCs made from exotic kinds of matter?

Yes. This is another "talk to a chemist". Ur doing it wrong, when halogens accumulate in your ozone layer. There seems to be no way to get them there, in extreme bulk, other than CFC release on the surface, or maybe some kind of insane doomsday weapon, both of which indicate extreme industrialization and a certain lack of ecological concern.

A standard/. automotive analogy is car sized lumps of unoxidized iron with certain precise and consistent fractions of dissolved carbon found on top of strips of heavy petroleum fractions mixed with gravel is just too weird geologically and biochemically to be anything but the product of intelligent life. You just don't find those elements laying around in that physical configuration.

you missed the joke I was trying to make: the summary was talking about the spectra being different from natural elements. As best we know, the elements (carbon, chlorine, etc.) on some distant planet world are identical, interchangeable, to those here on earth or anywhere else in the Universe. So, if we are looking for exotic spectra, we should be looking for those coming from exotic, not-naturally-occurring molecules. Talk to a chemist: if you're conflating elements with molecules, or claiming that one

car sized lumps of unoxidized iron with certain precise and consistent fractions of dissolved carbon found on top of strips of heavy petroleum fractions mixed with gravel is just too weird geologically and biochemically to be anything but the product of intelligent life.

The problem with CFC is that it's duration is an insignificant blip at cosmic scales. We've used it a little, we're phasing it out because it ruins a rather important layer of the atmosphere.

Our planet will continue to exist for about 5 billion years after the point where we reasonably reached a point that some aliens could contact at all without coming all the way here. (For most of our time on the planet we couldn't receive radio and didn't have telescopes.) Out of that, we've been abusing CFC heavily for maybe 50 years.

Let's say that t would take a while to get weaned off them, and for the upper atmosphere to gradually clear of them. Like maybe 500 years instead of 50. But it's still 500 years out of 5 billions.

That's a chance of of 1 in ten millions that if a civilization is there, you'll detect it by CFCs.

I think you missed the point about detecting CFCs. It's not about unintended terraforming of someone's home planet. It's about terraforming *another* planet that initially is a bit too cold for the civilisation in question. In human terms we are speaking about creating factories on Mars that pump CFCs into its atmosphere so as to create a more habitable (for us) climate there. See http://en.wikipedia.org/wiki/Terraforming_of_Mars#Using_fluorine_compounds [wikipedia.org]

I'm one of the scientists affiliated with this project. It's very true that SETI in general terms is a "needle in a haystack" sort of search. So one way to look at this is that we are suggesting more "needles" to look for. So far, we are searching for radio waves and optical pulses. Looking for technosignature molecules in a planetary atmosphere (if it actually works, which is what we are trying to figure out with our proposal), is a third needle.
I also totally agree with your points about looking for "

gigawatts of radio waves put into space: check
at a wavelength interesting to astronomers: check
low--frequency modulation, common phase: check (think Fourier analysis over months of data to filter out unmodulated light of a nearby star)
characteristic spectral fingerprint of artificial light: check
not limited to a civilisation's "radio window": check

Good point, though that only works for planets with a day/night cycle and aliens depending on sight during night.

And life that relies on sight at all. Life was on Earth a very long time without being sensitive to EM radiation. The majority of life on Earth still doesn't, to any significant effect. And there are comparatively intelligent creatures that rely predominantly on echolocation.

And light pollution measures and energy saving says that the streetlighting we've had for a mere fraction of a galactic second (i.e. a couple of hundred years) won't be here in that same fraction again.

Hell, as it is, we try to reduce the amount of light that goes somewhere unnecessary (e.g. the sky!) or that is produced and doesn't do anything. There are already countries and cities with lighting that's dynamic based on the cars rolling over it (which means the signal is even HARDER to find, even if you knew what you were looking for).

And in terms of the stretch of a civilisation, lighting visible even from orbit, let alone the other side of the galaxy, is literally a tiny flicker that you'll only catch if you're constantly listening to EXACTLY that, in EXACTLY the right place for a few billion years.

Hell, it's hard enough to see all of Earth's artificial lighting from orbit if there is cloud cover, let alone from somewhere like where Voyager currently is, and as you got further out the inverse square law solves the problem nicely to give you a probability of anyone detecting it tending rather swiftly towards zero.

If you want to detect a civilisation, about the only sensible thing to do is ignore the planets, look at the stars. Because sources of energy that huge, that well light-up, that stable, that predictable and, with suitable technology, even harvestable (I believe it's called a Dyson sphere) are likely to be something that won't stop being a commodity for a long time and activity on them will be inherently visible (even if that's by one-day disappearing entirely).

Think to yourself. I plonk you down into the universe at an unknown point and at an unknown time since the Big Bang. I give you a billion-year-long-life (sound a lot? It's not). How do you find someone who's had the same done to them? The chances are you're not even going to be able to see each other, would never be at the right stages at the right times to communicate with each other before moving onto the "next most advanced / obvious method of communication", and even if you do by some chance talk be too far away or your communication too "out of date" to do anything useful with it.

Until you can quite literally bend space and visit other places, it's all a bit pointless to be looking because of simple physical laws. And by the time you *can* do that, it's easier to just plonk a sensor on every star system with your space bending techniques than it would be to ever listen out for them all.

We are quite literally talking about how to detect a particular mayfly of interest on an entire planet of activity. And by the time we do it, that mayfly has evolved to build its own space program and buggered off deeper into the galaxy anyway.

gigawatts of radio waves put into space: check
at a wavelength interesting to astronomers: check
low--frequency modulation, common phase: check (think Fourier analysis over months of data to filter out unmodulated light of a nearby star)
characteristic spectral fingerprint of artificial light: check
not limited to a civilisation's "radio window": check

The intensity of nearly all signal we put out outside diminush so rapidely as to be non differentiable from galactic noise, within a few AU, maybe 1 LY at most. The only signal which has reached a few dozen LY was the one sent (when was it ? 70 ies ?) from a radio antena a very strong pulse directed at a place far away, and it was 2 times a one minute or two signal.
The rest ? Street light ? radio ? TV ? All noise beyond 1 light year.

Have you ever did any involved mathematical analysis of detecting a slowly drifting 50Hz signal in a background stronger by hundreds of dB? I did not. This is why I would not say "all noise". I just do not know that. Do you?

Our society is still too disorganized and prone to impulsive, selfish acts for us to contact an alien civilization.

If we don't immediately make war on them, we'll move in, set up a gift shop and a law firm, then start piping them our TV and selling them whatever junk food has taken over for the Twinkie (RIP).

If you were an alien civilization, and your first contact from outside came from the U.S. Congress and/or McDonald's, or maybe you were exposed to Justin Bieber or dubstep, you might just pull up the we

The prospect of finding an alien civilization that uses hairspray is not very good, given that Little Green Men rarely have hair in Hollywood or Roswell. However, CFCs are less likely to be an indicator of hairspray than plastic foam, circuit board manufacture [nytimes.com], Star Trek-esque hypospray propellent, refrigerators or air conditioning [nytimes.com]. The NY Times just ran an article about how we're still venting CFCs from home central air units in the U.S., over 20 years after the big marketing push to eliminate them.

We're already phasing out the use of CFCs and will likely not produce any detectable amounts in the near future. Don't they think aliens would learn the same lesson? Giving us, at most, a 100yr window to catch their CFC use? Why do people have this incredibly close minded view of alien life that makes them think that not only will they be like us, with arms and legs, be based on water but also be stuck in the same time period as us as well?

I suspect that we'll eventually find life on nearly all of the planets and even some of the asteroids in our own solar system. Maybe even intelligent life that's trapped under heavy atmosphere that really has had no technological way to explore space. Imagine an intelligent creature floating in the atmosphere of Jupiter or Saturn. They'd have almost no material to build tools out of, much less spacecraft or telescopes. And MOST planets have atmospheres like theirs.

The website you linked to isn't overly packed with peer-reviewed research ideas. My colleagues who study volcanic emissions and halocarbons do tell me that measurements of carbon tetrachloride (CCl4) (which the unscientific label of "honorary CFC" as it was regulated in the Montreal Protocol) may in fact be produced in extremely minor quantities by some volcanoes. This is cool as it points to new science. But the measured fluxes are 6 orders of magnitude lower than the anthropogenic fluxes. i.e. it doesn't

If you see a flux of CFCs in the atmosphere, why would you assume that this is due to anthropogenic activity?

More importantly, how would you exclude natural activity as a cause of observed CFC fluxes? One might start off with the assertion that CFCs never occur naturally, but as we've seen, that is demonstrably false. We could do some study of natural CFC sources, and try to extrapolate that to the entire universe of natural CFC sources, but that would be informative, not definitive.

Yes, thanks for this skepticism. In general the statement "x" is not produced naturally is false. Nature is surprisingly diverse and creative. For example one often sees statements like "dioxins don't occur in nature, or free chlorine doesn't occur in nature, or there is no natural equivalent to HFCS. These are false.

In reality what is important is the quantity of the materials, where they occur and what the environmental and health impacts are.

Hi all. I'm one of the scientists involved in this project. We are trying out this new kickstarter-for-science approach as it's both hard to get NASA funds for SETI, and it's also surprisingly hard to get small "seed money" type grants to do cutting edge work. We've started our own non-profit scientific research organization (http://bmsis.org) and are trying to do science outside the confines of the traditional academic structure. We'd love your support if you can (http://www.petridish.org/projects/do-aliens-use-hairspray) but more than that, we'd love to hear any ideas/answer questions about the project.

hmmn.. if intelligent aliens would have analyzed Earth's atmosphere 400yrs ago, as proposed, they would have dismissed it saying no life exists in our solar system.

In some ways that's easier because there is no requirement to only look once. They'd see all kinds of interesting atmospheric changes over a couple centuries, not just CFCs. Weathermen studying climate on distant planets will eventually be a growth industry.

You could have fun trying to list atmospheric changes over time. Hmm I'd say first you see lots of particulates from cruddy fire, like london smog in 1800. Then you'd see a lot of sulfur compounds. Then you'd see strange radioisotopes (probably too

Well even more to the point. There is the time we Made CFC's and the time we found out it was bad so we stopped using it, a 50-100 year gap. It may take a few hundred years for the chemical to degrade. But you may have a gap of a few hundred years in a planets billions year lifespan, to find evidence of intelligent life.

We are killing ourselves with our own pollution. This is due to our success as an animal. Every non-intelligent animal suffers population collapses due to population rising above sustainable levels. We are about there.We are killing ourselves with pollutants and "deskjobs" and plentiful food which is not what our bodies are adapted for.We are not acting any more intelligent than rats or crows.

No matter if they discovered us. They won't visit us, so far our science knows, they can't, no matter how advanced they are. They could send a signal, but need to be relatively close to both being able to detect us and send a signal with any kind of hope that we detect and understand it (and considering how much people like you is asking for basically banning space investigation, i'd say that the window of opportunity for that is closing).

There are at least two other plausible explanations for the Fermi paradox: 1) interstellar travel is really hard. 2) it is hard for technologically-advanced civilizations to last long. We have no evidence on 2, and the best evidence we have on 1 is in the affirmative.

3) Intelligence means they want to communicate with the savages. Think back to earths colonial era, how many average joes in England wanted to talk to or hang out with who they considered savages? Once you grow out of the cultural toddler era of religion, and grow out of the slavery and colonialism era, there is no intense demand to visit, meet, or talk to the savages, is there? So we'll have rich tourists and anthropologists visiting and watching us, both of who want to keep a low profile so they can st

5)...But it only takes a handful of explorers and malcontents to establish a colony, and available evidence is that evolution preferentially selects for organisms driven to reproduce. Admittedly though a species that managed to not wipe themselves out may have gotten those impulses under control, and/or an authoritarian government may be violently resistant to establishing colonies outside their control. Still the window for human-level civilizations to evolve has been open for billions of years, it seems

Actually I haven't heard much evidence for 1 either - they wouldn't need to travel fast, 0.001c would be plenty fast enough for an early-rising civilization to have colonize the entire galaxy by now, and conceptually at least a world-ship in a hollowed-out asteroid/moon would be fairly simple to construct and launch, and a couple miles of rock should provide plenty of shielding against anything life-threatening, especially if you assume it never accelerates significantly after getting up to speed, instead n

TOTAL FAIL
We are pretty smart - we made atom bombs and robots and all kinds of toys. So far faster-than-light travel totally eludes us. There literally could be 10,000 planets with 10,000 Einsteins per planet in our hood and no one is going anywhere.

Our sun is a comparative newcomer among 3rd-generation sun-like stars, the window for human-level civilizations to have evolved in our galaxy has been open for BILLIONS of years, plenty of time for a civilization to colonize the entire galaxy even if they never travel at even 1% of lightspeed.

Until WE do it I would think assuming others can do it is a bit silly. What if they are 98% as smart as us and their rockets blow up? What if they don't give a shit about flying in space? What if they all nuke themselves back to the stone age? Maybe we are the only ones to not play WW III when we get nukes? Maybe they are all a bunch of smart marine animals that can sing and do sonar like a mensa-whale but can't build anything? Maybe they did show up here and thought WE were a bunch of dangerous nutters and

the Milky Way is only 100,000 ly wide. Therefore, if there were alien life out there with advanced civilizations, they would find travelling such a small distance a piece of cake and would have discovered us by now.

To be advanced enought to get past lightspeed, we'd be chimps or less by comparison.

And Tegmark says if the whole galaxy we live in has no life, it's highly unlikely there's life any elsewhere, either

Not logical. It could well be that there are only one or two plaents in any given galaxy that is

You're not thinking in cosmic terms. Even if we ignore the rest of the universe outside our galaxy our planet is still 4.5 BILLION years old, and our sun was a relative latecomer to the party of 3rd-generation stars likely to have Earth-like planets - meaning there was plenty of time for human-level civilizations to develop elsewhere in our galaxy before our planet even formed. If life were common then at least one of those civilizations would likely have taken to the stars, and even if they only ever tra

Because nuke testing has only been around less than a hundred years. In universal scales, that's barely worth bothering with. It's literally a fleeting spark. The Sun is 4.6bn years old alone. Even from the Sun, it would have been a long wait to see some activity on earth that you could detect by looking for nukes (if they even have a signature that will travel across the galaxy which seems unlikely given that thousands of them have gone off across the globe in the past and we barely notice *here*, let

I'm one of the scientists involved in the project. We see this primarily as a search for terraformed worlds, rather than looking for inadvertent technological byproducts. We've started a kickstarter-like drive to do the fundamental research needed to find out if an actively terraformed world would be detectable over astronomical distances. Details are here: http://www.petridish.org/projects/do-aliens-use-hairspray [petridish.org]
-Mark

While I'm all for trying to find life on other planets, wouldn't it be far better to improve our space travel capabilities as well as creating some sort of Intergalactic Network

INTERGALACTIC?? Holy shit, man, the closest galaxy to ours is 11.7 million light-years away! You're going to wait 11.7 million years for a response? Where are you going to get the power to send a message that far, considering the inverse square law? If you meant intragalactic, the nearest star is four light years away. Do you have so

Not hairspray, evidence of terraforming, for which CFCs could be useful. I think the SETI folks are beginning to conclude that the chances of discovering a civilization via radio are miniscule - as efficiency improves in another couple centuries humanity probably won't have a significant radio footprint, and assuming a few-century transmission window we're unlikely to detect a signal unless radio-using civilizations are ridiculously common, or someone is specifically trying to talk to us (in which case they